Marine debris, also known as marine litter, is human-created waste that has deliberately or accidentally been released in a lake, sea, ocean or waterway. Floating oceanic debris tends to accumulate at the center of gyres and on coastlines,[1] frequently washing aground, when it is known as beach litter or tidewrack. Deliberate disposal of wastes at sea is called ocean dumping. Naturally occurring debris, such as driftwood, are also present.

With the increasing use of plastic, human influence has become an issue as many types of plastics do not biodegrade. Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts.[2] Dumping, container spillages, litter washed into storm drains and waterways and wind-blown landfill waste all contribute to this problem.

In efforts to prevent and mediate marine debris and pollutants, laws and policies have been adopted internationally. Depending on relevance to the issues and various levels of contribution, some countries have introduced more specified protection policies.

The US military used ocean dumping for unused weapons and bombs, including ordinary bombs, UXO, landmines and chemical weapons from at least 1919 until 1970.[7] Millions of pounds of ordnance were disposed of in the Gulf of Mexico and off the coasts of at least 16 states, from New Jersey to Hawaii (although these, of course, do not wash up onshore, and the US is not the only country who has practiced this).[8]

Eighty percent of marine debris is plastic.[9] Plastics accumulate because they typically do not biodegrade as many other substances do. They photodegrade on exposure to sunlight, although they do so only under dry conditions, as water inhibits photolysis.[10] In a 2014 study using computers models, scientists from the group 5 Gyres, estimate 5.25 trillion pieces of plastic weighing 269,000 tons dispersed in oceans in similar amount in the Northern and Southern Hemispheres, and one-hundredth of them in particles in the scale of a sand-size.[11]

8.8 million metric tons of plastic waste are dumped in the world's oceans each year. Asia was the leading source of mismanaged plastic waste, with China alone accounting for 2.4 million metric tons.[13][14]

Plastic waste has reached all the world's oceans. This plastic pollution harms an estimated 100,000 sea turtles and marine mammals and 1,000,000 sea creatures each year.[15] Larger plastics (called "macroplastics") such as plastic shopping bags can clog the digestive tracts of these larger animals when consumed by them[16] and can cause starvation through restricting the movement of food, or by filling the stomach and tricking the animal into thinking it is full. Microplastics on the other hand harm smaller marine life. Pelagic plastic pieces in the center of our ocean’s gyres for example outnumber live marine plankton, and are passed up the food chain to reach all marine life.[17] A 1994 study of the seabed using trawl nets in the North-Western Mediterranean around the coasts of Spain, France and Italy reported mean concentrations of debris of 1,935 items per square kilometre. Plastic debris accounted for 77%, of which 93% was plastic bags.[16]

Nurdles, also known as "mermaids' tears", are plastic pellets, typically under five millimetres in diameter, that are a major component of marine debris. They are a raw material in plastics manufacturing, and enter the natural environment when spilled. Weathering produces ever smaller pieces. Nurdles strongly resemble fish eggs.[18]

Litter, made from diverse materials that are denser than surface water (such as glasses, metals and some plastics), have been found to spread over the floor of seas and open oceans, where it can become entangled in corals and interfere with other sea-floor life, or even become buried under sediment, making clean-up extremely difficult, especially due to the wide area of its dispersal compared to shipwrecks. Research performed by MBARI found items including plastic bags below 2000m depth off the west coast of North America and around Hawaii.[19]

In Halifax Harbour, Nova Scotia, 52% of items were generated by recreational use of an urban park, 14% from sewage disposal and only 7% from shipping and fishing activities.[23] Around four fifths[24] of oceanic debris is from rubbish blown onto the water from landfills, and urban runoff.[25] In the 1987 Syringe Tide, medical waste washed ashore in New Jersey after having been blown from Fresh Kills Landfill.[26][27] On the remote sub-Antarctic island of South Georgia, fishing-related debris, approximately 80% plastics, are responsible for the entanglement of large numbers of Antarctic fur seals.[28]

The currents of the North Pacific Gyre spiral inwards, depositing debris in the convergence zone

Once waterborne, debris becomes mobile. Flotsam can be blown by the wind, or follow the flow of ocean currents, often ending up in the middle of oceanic gyres where currents are weakest. The Great Pacific Garbage Patch is one such example of this, comprising a vast region of the North Pacific Ocean rich with anthropogenic wastes. Estimated to be double the size of Texas, the area contains more than 3 million tons of plastic.[30] In fact, patches may be large enough to be picked up by satellites. For example, when the Malaysian Flight MH370, disappeared in 2014, satellites were scanning the oceans surface for any sign of it, and instead of finding debris from the plane they came across floating garbage.[31] The gyre contains approximately six pounds of plastic for every pound of plankton.[32] The oceans may contain as much as one hundred million tons of plastic.[24] It is estimated that each garbage patch in the ocean have up to one million tons of trash swirling around in them, sometimes extending down to around one hundred feet below the surface.[33] Some items that have been extracted from these garbage patches are: a drum of hazardous chemicals, plastic hangers, tires, cable cords, a ton of tangled netting etc.

Over 40% of oceans are classified as subtropical gyres, a fourth of the planets surface area has become an accumulator of floating plastic debris.

Islands situated within gyres frequently have coastlines flooded by waste that washes ashore; prime examples are Midway[34] and Hawaii.[35] Clean-up teams around the world patrol beaches to attack this environmental threat.[34]

Many animals that live on or in the sea consume flotsam by mistake, as it often looks similar to their natural prey.[36] Bulky plastic debris may become permanently lodged in the digestive tracts of these animals, blocking the passage of food and causing death through starvation or infection.[37] Tiny floating plastic particles also resemble zooplankton, which can lead filter feeders to consume them and cause them to enter the ocean food chain. In samples taken from the North Pacific Gyre in 1999 by the Algalita Marine Research Foundation, the mass of plastic exceeded that of zooplankton by a factor of six.[9][38]

The hydrophobic nature of plastic surfaces stimulates rapid formation of biofilms,[40] which support a wide range of metabolic activities, and drive succession of other micro- and macro-organisms.[41]

Concern among experts has grown since the 2000s that some organisms have adapted to live on[42] floating plastic debris, allowing them to disperse with ocean currents and thus potentially become invasive species in distant ecosystems.[43] Research in 2014 in the waters around Australia[40] confirmed a wealth of such colonists, even on tiny flakes, and also found thriving ocean bacteria eating into the plastic to form pits and grooves. These researchers showed that "plastic biodegradation is occurring at the sea surface" through the action of bacteria, and noted that this is congruent with a new body of research on such bacteria. Their finding is also congruent with the other major research undertaken[44] in 2014, which sought to answer the riddle of the overall lack of build up of floating plastic in the oceans, despite ongoing high levels of dumping. Plastics were found as microfibres in core samples drilled from sediments at the bottom of the deep ocean. The cause of such widespread deep sea deposition has yet to be determined.

Not all anthropogenic artifacts placed in the oceans are harmful. Iron and concrete structures typically do little damage to the environment because they generally sink to the bottom and become immobile, and at shallow depths they can even provide scaffolding for artificial reefs. Ships and subway cars have been deliberately sunk for that purpose.[45]

Additionally, hermit crabs have been known to use pieces of beach litter as a shell when they cannot find an actual seashell of the size they need.[46]

Skimmer boat used to remove floating debris and trash from the Potomac and Anacostia rivers

Techniques for collecting and removing marine (or riverine) debris include the use of debris skimmer boats (pictured). Devices such as these can be used where floating debris presents a danger to navigation. For example, the US Army Corps of Engineers removes 90 tons of "drifting material" from San Francisco Bay every month. The Corps has been doing this work since 1942, when a seaplane carrying Admiral Chester W. Nimitz collided with a piece of floating debris and sank, costing the life of its pilot.[47] Once debris becomes "beach litter", collection by hand and specialized beach-cleaning machines are used to gather the debris.

Elsewhere, "trash traps" are installed on small rivers to capture waterborne debris before it reaches the sea. For example, South Australia's Adelaide operates a number of such traps, known as "trash racks" or "gross pollutant traps" on the Torrens River, which flows (during the wet season) into Gulf St Vincent.[48]

In lakes or near the coast, manual removal can also be used. Project AWARE for example promotes the idea of letting dive clubs clean up litter, for example as a diving exercise.[49]

On the sea, the removal of artificial debris (i.e. plastics) is still in its infancy. However some projects have been started which used ships with nets (Kaisei and New Horizon) to catch some plastics, primarily for research purposes. Another method to gather artificial litter has been proposed by Boyan Slat. He suggested using platforms with arms to gather the debris, situated inside the current of gyres.[50]

Another issue is that removing marine debris from our oceans can potentially cause more harm than good. Cleaning up micro-plastics could also accidentally take out plankton, which are the main lower level food group for the marine food chain and over half of the photosynthesis on earth.[31] One of the most efficient and cost effective ways to help reduce the amount of plastic entering our oceans is to not participate in using single use plastics, avoid plastic bottled drinks such as water bottles, use reusable shopping bags, and to buy products with reusable packaging.[51]

The ocean is a global common, so negative externalities of marine debris are not usually experienced by the producer. In the 1950s, the importance of government intervention with marine pollution protocol was recognized at the First Conference on the Law of the Sea[60].

MARPOL 73/78 – a convention designed to minimize pollution of the seas, including dumping, oil and exhaust pollution[63] The original MARPOL convention did not consider dumping from ships, but was revised in 1978 to include restrictions on marine vessels[64].

UNCLOS- signed in 1982, but effective in 1994, United Nations Convention on the Law of the Sea emphasized the importance of protecting the entire ocean and not only specified coastal regions[60]. UNCLOS enforced restrictions on pollution, including a stress on land-based sources[60]. Regulations imposed by this agreement have potential to help mediate effects of climate change[65].

In the waters of the United States, there have been many observed consequences of pollution including: hypoxic zones, harmful agal blumes, and threatened species[69]. In 1972, the United States Congress passed the Ocean Dumping Act, giving the Environmental Protection Agency power to monitor and regulate the dumping of sewage sludge, industrial waste, radioactive waste and biohazardous materials into the nation's territorial waters.[70] The Act was amended sixteen years later to include medical wastes.[71] It is illegal to dispose of any plastic in US waters.[72]

A large number of groups and individuals are active in preventing or educating about marine debris. For example, 5 Gyres is an organization aimed at reducing plastics pollution in the oceans, and was one of two organizations that recently researched the Great Pacific Garbage Patch. Heal the Bay is another organization, focusing on protecting California's Santa Monica Bay, by sponsoring beach cleanup programs along with other activities. Marina DeBris is an artist focusing most of her recent work on educating people about beach trash. Interactive sites like Adrift[74] demonstrate where marine plastic is carried, over time, on the worlds ocean currents. On April 11, 2013 in order to create awareness, artist Maria Cristina Finucci founded The Garbage patch state at UNESCO[75] –Paris in front of Director General Irina Bokova . First of a series of events under the patronage of UNESCO and of Italian Ministry of the Environment.[76]

Forty-eight plastics manufacturers from 25 countries, are members of the Global Plastic Associations for solutions on Marine Litter, have made the pledge to help prevent marine debris and to encourage recycling.[31]

^Craig, R. (2005). PROTECTING INTERNATIONAL MARINE BIODIVERSITY: INTERNATIONAL TREATIES AND NATIONAL SYSTEMS OF MARINE PROTECTED AREAS. Journal of Land Use & Environmental Law, 20(2), 333-369. Retrieved from https://www.jstor.org/stable/42842976